RECLAMATION EXHIBIT. Managing Water in the West. SECURE Water Act Section 9503(c) Reclamation Climate Change and Water 2011.

Transcription

1 RECLAMATION EXHIBIT Managing Water in the West I N1ELCl5 SECURE Water Act Section 9503(c) Reclamation Climate Change and Water U.S. Department of the Interior Policy and Administration - - Bureau of Reclamation Denver, Colorado April

2 Mission Statements The U.S. Department of the Interior protects America s natural resources and heritage, honors our cultures and tribal communities, and supplies the energy to power our future. The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public.

3 Reclamation SECURE Water Act Section 9503(c) Reclamation Climate Change and Water Prepared for: United States Congress Prepared by: U.S. Department of the Interior Bureau of Reclamation Citation: Reclamation, SECURE Water Act Section 9503(c) Congress, Authors, Contributors, and Editors (in alphabetical order): Climate Change and Water, Report to Alexander, Patty; Brekke, Levi; Davis, Gary; Gangopadhyay, Subhrendu; Grantz, Katrina; Hennig, Charles; Jerla, Carly; Llewellyn, Dagmar; Miller, Paul; Pruitt, Tom; Raff, David; Scott, Tom; Tansey, Michael; Turner, Toni Bureau of Reclamation Denver, Colorado April

4

5 SECURE SECURE EXECUTIVE SUMMARY Background Established in 1902, the Bureau of Reclamation (Reclamation) is best known for the dams, powerplants, and canals it constructed within the 17 Western United States. Today, Reclamation is the largest wholesaler of water in the United States and the second largest producer of hydroelectric power in the Western United States. Reclamation s mission is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Reclamation s vision is to protect local economies and preserve natural resources and ecosystems through the effective use of water. This vision is achieved through Reclamation s leadership, use of technical expertise, efficient operations, and responsive customer service. In meeting its mission, Reclamation s planning and operations rely upon assumptions of present and future water supplies based on climate. Climate information influences the evaluation of resource management strategies through assumptions or characterization of future potential temperature, precipitation, and runoff conditions, among other weather information. Water supply estimates are developed by determining what wet, dry, and normal periods may be like in the future and by including the potential for hydrologic extremes that can create flood risks and droughts. Water demand estimates are developed across water management system uses, including both the natural and socioeconomic systems, which include agriculture, municipal, environmental, and hydroelectric power generation. System operation boundaries include the natural system and the socioeconomic system. Acknowledging the uncertainties associated with future climate and associated potential impacts, the Omnibus Public Land Management of 2009 (Public Law ) Subtitle F Water authorized Reclamation to continually evaluate and report on the risks and impacts from a changing climate and to identify appropriate adaptation and mitigation strategies utilizing the best available science in conjunction with stakeholders. SECURE Water and Reclamation s Response The Omnibus Public Land Management Act of 2009 (Public Law ) Subtitle F Water was passed into law on March 30, Also known as the SECURE Water Act, the statute establishes that Congress finds that adequate and safe supplies of water are fundamental to the health, economy, security, and ecology of the United States although global climate change poses a III

6 each the each each Secure Water Act Section 9503(c) significant challenge to the protection of these resources. Congress also finds that data, research, and development will help ensure future water supplies and that, although States bear the primary responsibility and authority for managing the water resources of the United States, the Federal Government should support the States, as well as regional, local, and tribal governments in this endeavor. With a focus on Reclamation s role as a Federal agency conducting water management and related activities, Reclamation is assessing risks to the water resources of the Western United States and developing strategies to mitigate risks to help ensure that the long-term water resources management of the United States is sustainable. Section 9503 of the SECURE Water Act identifies the Reclamation Climate Change and Water Program. Reclamation is addressing the authorities within the SECURE Water Act through a broad set of activities in conjunction with Secretarial Order 3289 establishing the U.S. Department of the Interior s integrated approach to addressing climate change and Secretarial Order 3297 establishing the WaterSMART Program and Research and Development activities all of which working in a coordinated manner with other Federal agencies, State, local, and tribal governments and nongovernmental organizations. Reclamation s activities represent a comprehensive and coordinated approach to identifying risks and impacts associated with current and future climate, working with stakeholders to identify and implement adaptation and mitigation strategies and collaborating to identify the best available science. About this Report This report is prepared by Reclamation in fulfillment of the requirements within section () 9503 of the SECURE Water Act. This report addresses the elements of 9503 part (c), which are: (c)(l) effect of and risk resulting from, global climate change with respect to the quantity of water resources located in each major Reclamation river basin (c)(2) impact of global climate change with respect to the operations of the Secretary in each major Reclamation river basin (c)(3) mitigation and adaptation strategy considered and implemented by the Secretary of the Interior to address each effect of global climate change (c)(4) coordination activity conducted by the Secretary with the U.S. Geological Survey (USGS), National Oceanic and iv

7 Atmospheric Administration (NOAA), U.S. Department of Agriculture (USDA), or any appropriate State water resource agency This report is Reclamation s first report under the authorities of the SECURE Water Act and presents the current information available. Future reports will build upon the level of information currently available and the rapidly developing science relevant to address the authorities within the SECURE Water Act. Much of this report is based on synthesizing available literature and summarizing key findings from peer-reviewed studies. However, for element (c)(l), which includes focus on climate change implications for snowpack and natural hydrology, findings from an original assessment are introduced, as this assessment has been conducted consistently for the eight Reclamation river basins, framed by a consistent set of Western United States climate projections. The report is based on making comprehensive and consistent assessments of risk across each of the major eight basins in a portfolio manner. Thus, results are comparable across the river basins assessed and, therefore, may support local level impact assessment; but further information likely is needed to inform local level decisionmaking. There are many other activities underway, focused on basin specific efforts in coordination with Reclamation stakeholders. Activities, including fiscal year (FY) 2009 WaterSMART Basin Studies (Colorado River Basin, Yakima River basin, Milk-St. Mary s River basin), the River Management Joint Operating Committee working within the Columbia River Basin, and the California Bay-Delta Conservation Plan as examples, may make different assumptions of how to include climate information, how to address uncertainties, and how to present results. Care must be taken to evaluate past and future time periods of comparisons and methodological choices when comparing the results presented within this report to other activities. The report is organized as follows: Section 1: Provides an introduction and a brief overview to projected climate changes over the Western United States and implications for snowpack, runoff amount, and runoff timing (or seasonality). Section 1 also provides how the information for this report was developed as well as the uncertainties associated with the information. Sections 2 through 8: Provide basin-specific discussions of each major Reclamation basin identified within the SECURE Water Act including the basin setting, basin specific coordination, historical climate, historical Reclamation.. West- Wide Climate Risk Assessments: Bias Corrected and Spatially Downscaled Suiface Water Projections. V

8 hydrology, projected future climate and hydrology, and implications for various water and environmental resources. Note that the SECURE Water Act separately identifies the Sacramento and San Joaquin Rivers as reporting basins; however, in this report, these two basins are discussed in concert given the interwoven nature of their water management issues (section 7). Section 9: Integrates findings from the basin-specific discussion to provide a west-wide perspective on projected climate and hydrologic changes. Geographic variations in projected changes are highlighted. The section also provides a brief inventory of uncertainties affecting the interpretation of these results, ranging from the uncertainties of generating global climate projections to simulating local hydrologic response. Section 10: Describes Reclamation s coordination of activities with respect to the SECURE Water Act Authorities. Section 11: Provides adaptation actions being implemented. This section provides a description of Reclamation activities with targets within the Department of the Interior High Priority Performance Goal for Climate. Section 12: Provides a listing references used within this document, directing the audience to a source for additional information. Key Findings of this Report to Congress A recent paper by the Congressional Budget Office 2 summarizes the current understanding of the impacts of climate change in the United States, including that warming will tend to be greater in the interior of the contiguous United States. Temperature and precipitation conditions over Western United States regional drainages are projected to change as the effects of global climate change are realized. Projections of future temperature and precipitation are based on multiple Global Circulation (or Climate) Models (GCM5) and various projections of future greenhouse gas emissions (GHG), technological advancements, and global population estimates. A survey of these models over any of the regional drainages shows that there is model consensus agreement reported between climate model projections 2 Congressional Budget Office (CBO) Potential Impacts ofclimate Change in the United States. Prepared at the request of the Chairman of the Senate Committee on Energy and Natural Resource. May vi

9 that temperatures will increase during the century. There is less model consensus on the direction of precipitation change, with some climate models suggesting decreases while others suggest increases, although greater consensus does exist for some geographic locations (e.g., model consensus towards wetter conditions approaching the Northwestern United States and northern Great Plains and model consensus towards drier conditions approaching the Southwestern United States). These findings are consistent with the historical and projected future climate information used in this report. Much of the Western United States has experienced warming during the century (roughly 2 degrees Fahrenheit ( F) in the basins considered within this report) and is projected to experience further warming during the century with central estimates varying from roughly 5 7 F, depending on location. As related to precipitation, historical trends in annual conditions are less apparent. Future projections suggest that the Northwestern and north-central portions of the United States gradually may become wetter (e.g., Columbia Basin and Missouri River basin) while the Southwestern and south-central portions gradually become drier (e.g., San Joaquin, Truckee, and Rio Grande River basins and the Middle to Lower Colorado River Basin). Areas in between these contrasts have median projected changes closer to no change, meaning they have roughly equal chances of becoming wetter or drier (e.g., Kiamath and Sacramento basins and the Upper Colorado Basin). Note that these summary statements draw attention to median projected changes in temperature and precipitation, characterized generally across the Western United States. Inspection of the underlying ensemble of projection information shows that there is significant variability and uncertainty about these projected conditions both geographically and with time. st 21 2O These historical and projected climate changes have implications for hydrology. Focusing first on snow accumulation and melt, warming trends appear to have led to a shift in cool season precipitation towards more rain and less snow, which has caused increased rainfall-runoff volume during the cool season accompanied by less snowpack accumulation in some Western United States locations. Hydrologic analyses-based future climate projections suggest that warming and associated loss of snowpack will persist over much of the Western United States. However, there are some geographic contrasts. Snowpack losses are projected to be greatest where the baseline climate is closer to freezing thresholds (e.g., lower lying valley areas and lower altitude mountain ranges). It also appears that, in high altitude and high latitude areas, there is a chance that cool season snowpack actually could increase during the 2 century (e.g., Columbia headwaters in Canada, Colorado 1st 2l vii

10 headwaters in Wyoming), because precipitation increases are projected and appear to offset the snow-reduction effects of warming in these locations. Geographic implications for future runoff are more complex than those for future snowpack. Although historical trends in annual or seasonal runoff appear to be weak, hydrologic analyses based on future climate projections suggest that geographic trends should emerge as projected climate change develops. For example, the Southwestern United States to Southern Rockies are projected to experience gradual runoff declines during the 21 st century (e.g., Rio Grande River basins and the Colorado River Basin) while the Northwest to north central United States are projected to experience little change through mid-2 1st century to increases by late-2 1st century (e.g., Columbia River Basin and Missouri River basin). Seasonally speaking, warming is projected to affect snowpack conditions as discussed above. Without precipitation change, this would lead to increases in cool season rainfall-runoff and decreases in warm season snowmelt-runoff. Results show that the degree to which this plays out varies by location in the Western United States. For example, cool season runoff is projected to increase over the west coast basins from California to Washington and over the northcentral United States (e.g., San Joaquin, Sacramento, Truckee, Kiamath, and Missouri basins and the Columbia Basin) and to experience little change to slight decreases over the Southwestern United States to Southern Rockies (e.g., Colorado River Basin and Rio Grande River basin). Warm season runoff is projected to experience substantial decreases over a region spanning southern Oregon, the Southwestern United States, and Southern Rockies (e.g., Klamath, Sacramento, San Joaquin, Truckee, and Rio Grande River basins and the Colorado River Basin). However, north of this region, warm season runoff is projected to experience little change to slight increases (e.g., Columbia River Basin and Missouri River basin). It seems evident that projected increasing precipitation in the northern tier of the Western United States serves somewhat to neutralize warming-related decreases in warm season runoff whereas projected decreasing precipitation in the southern tier of the Western United States serves to amplify such warming-related decreases in warm season runoff. While these results indicate how annual and seasonal natural runoff might be altered under climate change and in ways that geographically vary, it is not possible to infer water management impacts from simply these natural runoff changes alone. Water management systems across the West have been designed to operate within envelopes of hydrologic variability, handling variations from season to season and year to year. These systems were designed with local hydrologic variability in mind; and, as a result, their physical and operating characteristics vary in terms of storage capacity and conveyance flexibility. For example, the Colorado River Basin has a relatively large degree of VIII

11 storage relative to annual runoff when compared to California River basins and particularly relative to the Columbia River Basin. The ability to use storage resources to control future hydrologic variability and changes in runoff seasonality is an important consideration in assessing potential water management impacts due to natural runoff changes. Within this report, there is a significant difference between the types of information presented with respect to risks from climate change on snowpack, hydrology, and water supplies and risks related to demand changes and the combined impacts on Reclamation s mission responsibilities. For example, the supply side is presented in a quantitative fashion with change metrics presented on annual runoff and seasonality of runoff. In contrast, for risks from demands and overall impacts, qualitative statements are made from literature synthesis at this time. Assessment of these water management impacts on a local level is a subject of ongoing activities within Reclamation s Basin Studies Program (Basin Studies and West-Wide Climate Risk Assessments) and other activities. Finally, while this report summarizes potential future climate and hydrologic conditions based on best available datasets and data development methodologies, there are a number of analytical uncertainties that are not reflected in this report s characterization of future hydroclimate possibilities. Such uncertainties arise from analyses associated with characterizing future global climate forcings such as greenhouse gas emissions, simulating global climate response to these forcings, correcting global climate model outputs for biases, spatially downscaling global climate model outputs to basin-relevant resolution, and characterizing regional to basin hydrologic response to such downscaled climate projection information. Collaborations Reclamation collaborates with many entities to carry out its mission responsibilities, including other Federal agencies, States, and local governments as well as tribes and non-governmental organizations. To fulfill the authorities within the SECURE Water Act, a consistent process has been developed and utilized to begin the process of evaluating risks and impacts through collaboration with Federal agencies and their stakeholders. This includes Research and Development collaborations with the U.S. Geological Survey, National Oceanic and Atmospheric Administration, U.S. Army Corps of Engineers, and others through the Climate Change and Water Working Group. Other key collaborators include the National Drought Information System, State Climatologists, and the Western States Water Council and Western Governors Association. Reclamation also is implementing Secretarial Orders 3289 and 3297 to establish the integrated ix

12 approach of addressing climate change and the WaterSMART Program. These two Secretarial Orders encourage collaboration with other Federal agencies, States, tribes, and local governments through sustainable water strategies and establishment of the Landscape Conservation Cooperatives and Climate Science Centers. Additional basin specific collaborations exist and are vital to the management of each basin identified within this report. x

13 Contents Page Executive Summary iii 1. Introduction 1.1 About Reclamation 1.2 Role of Climate Information in Reclamation s Water Resources Management About SECURE Water Act Section 9503: Reclamation Climate Change and Water Program About the Program About this Report Uncertainties Basin Report: Colorado Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Columbia Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Klamath Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Missouri Basin Setting Historical Climate 85 xi

14 Contents (contents) Page 5.3 Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Rio Grande Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Sacramento and San Joaquin Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources Basin Report: Truckee Basin Setting Historical Climate Historical Hydrology Future Changes in Climate and Hydrology Future Implications for Water and Environmental Resources West-wide Summary of Hydroclimate Changes Coordination Adaptation Actions References 193 xii

15 List of Figures Page Figure 1. Eight major Reclamation River Basins listed in the SECURE Water Act, Section Figure 2. Projected median temperature change in degrees Fahrenheit ( F)(of 112 climate projections) over the Western United States, relative to Figure 3. Projected median percentage precipitation change (of 112 climate projections) over the Western United States, relative to Figure 4. Approach to displaying results in this report (focus on median changes, left panel) versus Reclamation 201 la (focus on range of changes, right panel, showing percentile, median, 75 percentile changes) 15 th Figure 5. Colorado River Basin and runoff-reporting locations for this report 17 Figure 6. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Colorado River Basin above Lake Mead 21 Figure 7. Simulated annual climate averaged over Colorado River subbasins 26 Figure 8. Simulated decade-mean temperature over the Colorado River Basin above Yuma, Arizona 27 Figure 9. Simulated decade-mean precipitation over the Colorado River Basin above Yuma, Arizona 29 Figure 10. Simulated decade-mean April snowpack over the Colorado River Basin above Yuma, Arizona 30 Figure Il. Simulated changes in decade-mean runoff for several subbasins in the Colorado River Basin 32 Figure 12. Simulated annual maximum and minimum week runoff for several subbasins in the Colorado River Basin 34 Figure 13. Columbia River Basin above The Dalles and runoff-reporting locations for this report 41 Figure 14. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Columbia River Basin above The Dalles 44 1t XIII

16 List of Figures (continued) Page Figure 15. Simulated annual climate averaged over the Columbia River Basin and Snake River subbasin 47 Figure 16. Simulated decade-mean temperature over the Columbia River Basin above The Dalles 49 Figure 17. Simulated decade-mean precipitation over the Columbia River Basin above The Dalles 50 Figure 18. Simulated decade-mean April jst snowpack over the Columbia River Basin above The Dalles 51 Figure 19. Simulated changes in decade-mean runoff for several subbasins in the Columbia River Basin 53 Figure 20. Simulated annual maximum and minimum week runoff for several subbasins in the Columbia River Basin 55 Figure 21. Klamath River basin and runoff-reporting Locations for this report 63 Figure 22. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Klamath River Region 66 Figure 23. Simulated annual climate averaged over Kiamath River subbasins 69 Figure 24. Simulated decade-mean temperature over the Klamath River basin above Klamath, California 70 Figure 25. Simulated decade-mean precipitation over the Klamath River basin above Klamath, California 71 Figure 26. Simulated decade-mean April 1st Snowpack over the Kiamath River basin above Klamath, California 73 Figure 27. Simulated changes in decade-mean Runoff for several subbasins in the Klamath River basin above Klamath, California 74 Figure 28. Simulated annual maximum and minimum week runoff for several subbasins in the Klamath River basin 76 Figure 29. Missouri River basin and runoff-reporting Locations for this report 83 Figure 30. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Missouri Basin above Lake Oahe 86 xiv

17 List of Figures (continued) Page Figure 3 1. Simulated annual climate averaged over Missouri River subbasins 90 Figure 32. Simulated decade-mean temperature over the Missouri River above Omaha, Nebraska 91 Figure 33. Simulated decade-mean precipitation over the Missouri River above Omaha, Nebraska 92 Figure 34. Simulated decade-mean April 1st snowpack over the Missouri River above Omaha, Nebraska 93 Figure 35. Simulated changes in decade-mean runoff for several subbasins in the Missouri River basin 94 Figure 36. Simulated annual maximum and minimum week runoff for several subbasins in the Missouri River basin 96 Figure 37. Rio Grande basin, Pecos River basin, and runoffreporting locations for this report 105 Figure 38. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Rio Grande basin above Elephant Butte 109 Figure 39. Simulated annual climate averaged over Rio Grande subbasins 112 Figure 40. Simulated decade-mean temperature over the Rio Grande basin above Elephant Butte 113 Figure 41. Simulated decade-mean precipitation over the Rio Grande basin above Elephant Butte 114 Figure 42. Simulated decade-mean April 1st snowpack over the Rio Grande basin above Elephant Butte 116 Figure 43. Simulated changes in decade-mean runoff for several subbas ins in the Rio Grande basin 118 Figure 44. Simulated annual maximum and minimum week runoff for several subbasins in the Rio Grande River basin 119 Figure 45. Sacramento River, San Joaquin River, Tulare basin, and runoff-reporting locations for this report 127 Figure 46. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Sacramento River basin 132 xv

18 List of Figures (continued) Page Figure 47. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the San Joaquin River basin 133 Figure 48. Simulated annual climate averaged over Sacramento and San Joaquin River subbasins 138 Figure 49. Simulated decade-mean temperature over the Sacramento River basin above Freeport, California 139 Figure 50. Simulated decade-mean temperature over the San Joaquin River basin above Vernalis, California 140 Figure 51. Simulated decade-mean temperature over the Sacramento River basin above Freeport, California 141 Figure 52. Simulated decade-mean temperature over the San Joaquin River basin above Vernalis, California 142 Figure 53. Simulated decade-mean April 1st snowpack over the Sacramento River basin above Freeport, California 144 Figure 54. Simulated decade-mean April 1St snowpack over the San Joaquin River basin above Vernalis, California 145 Figure 55. Simulated changes in decade-mean runoff for several subbasins in the Sacramento and San Joaquin River basins 146 Figure 56. Simulated annual maximum and minimum week runoff for several subbasins in the Sacramento and San Joaquin River basins Figure 57. Truckee River basin, Carson River basins, and runoff-reporting locations for this report 157 Figure 58. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Truckee River region 161 Figure 59. Simulated annual climate averaged over Truckee and Carson River subbasins 164 Figure 60. Simulated decade-mean temperature over the Truckee River basin above Nixon 166 Figure 61. Simulated decade-mean precipitation over the Truckee River basin above Nixon 167 Figure 62. Simulated decade-mean April snowpack over the Truckee River basin above Nixon 168 xvi

19 List of Figures (continued) Page Figure 63. Simulated changes in decade-mean runoff for several subbasins in the Truckee and Carson River basins 170 Figure 64. Simulated annual maximum and minimum week runoff for several subbasins in the Truckee and Carson River basins 172 Figure 65. Projected snowpack changes distributed over the West 180 Figure 66. Change in percentage mean annual runoff distributed over the West 181 Figure 67. Change in percentage mean December March and mean April July runoff distributed over the West 183 List of Tables Table 1. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Colorado River Basin 35 Table 2. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Columbia River Basin 56 Table 3. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Kiamath River basin 77 Table 4. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Missouri River basin 98 Table 5. Summary of Simulated Changes in Decadal Hydroclimate for several subbasins in the Rio Grande Basin 120 Table 6. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Sacramento and San Joaquin River basins 150 Table 7. Summary of simulated changes in decade-mean hydroclimate for several subbasins in the Truckee and Carson River subbasins 173 xvii

20 6. Basin Report: Rio Grande 6.1 Basin Setting The Rio Grande basin is located in the Southwestern United States and serves as a source of water for irrigation, domestic, environmental and recreational uses in the States of Colorado, New Mexico, and Texas as well as in Mexico (figure 37). The Rio Grande headwaters are in the San Juan Mountains of southern Colorado. The river flows southward through New Mexico, and then southeastward as it forms the international boundary between Texas and Mexico before ultimately flowing into the Gulf of Mexico. The total river length is 1,896 miles, and it flows through the cities of Albuquerque, Las Cruces, El Paso, and Cuidad Juarez, draining a total of approximately 182,200 square miles. Basin topography varies from the mountains and gorges of the headwaters to the Bosque and high desert of central New Mexico, to deserts and subtropical terrain along the boundary between Texas and Mexico. The focus of this section of the report is with respect to the upper Rio Grande basin. 1 1OOW Figure 37. this report. Upper Rio Grande basin, Pecos River basin, and runoff-reporting locations for 105

21 The Upper Rio Grande facilities are operated by Reclamation and USACE with input from numerous stakeholders. Water operations staff from both agencies as well as the Middle Rio Grande Conservancy District, U.S. Fish and Wildlife Service, and other interested parties hold daily water operations conference calls during the irrigation season to discuss what water is needed, where it is needed, how it will move through the system, and impacts to the Endangered Species Act- (ESA) listed species. These calls discuss releases by Reclamation from Heron and El Vado Reservoirs in northern New Mexico and releases by USACE at Abiquiu and Cochiti Reservoirs to meet flow needs of the Middle Rio Grande. Reclamation and USACE work closely with the Middle Rio Grande Collaborative Program that includes 16 Federal, State, and local governmental entities, Indian tribes and pueblos, and nongovernmental organizations representing diverse interests. A 10-year Biological Opinion issued by U.S. Fish and Wildlife Service provides for releases to meet the needs of the ESA-listed silvery minnow. With respect to climate change, Reclamation is currently developing an impact assessment within the WaterSMART Basin Study Program West-Wide Climate Risk Assessments to support identification of impacts from climate change on the resources within the basin. Reclamation will be working with the States to communicate and coordinate this activity. Climate varies across the Rio Grande basin. Most of the basin is arid or semi arid, generally receiving less than 10 inches of precipitation per year. In contrast, some of the high mountain headwater areas receive on average over 40 inches of precipitation per year. Most of the total annual flow in the Rio Grande basin results, ultimately, from runoff from mountain snowmelt. Snowmelt processes result in Upper Rio Grande streamfiows, from the headwaters to Elephant Butte Reservoir, that peak in the late spring and early summer and diminish rapidly by midsummer. In the reach below Elephant Butte Reservoir and in the Lower Rio Grande, the supply comes directly from storage reservoirs, which may contain water from snowmelt and local inflows in current and past years. The hydrograph in the Lower Rio Grande is, therefore, determined by reservoir operations rather than snowmelt timing and duration. During the summer and fall, monsoon thunderstorms in the central New Mexico and Texas portions of the basin can produce additional peak flows in the river. However, these flows are usually smaller in volume than the snowmelt peaks and also of much shorter duration. The Rio Grande serves as the primary source of water for agriculture throughout the Rio Grande Valley, as well as the major municipalities along the river corridor. The river also supports unique fisheries and riparian ecosystems along 106

22 much of its length. The river is heavily utilized, and the river channel size is significantly smaller in the Lower Rio Grande than it is in the Upper Rio Grande. In recent years, intermittent and low flows have occurred in the lower reaches, and river flows do not reach the Gulf of Mexico every year. Along with water quantity, other important issues in the Rio Grande basin include threatened and endangered species and water quality. The Rio Grande is governed by the Rio Grande Compact, which was approved by Congress in 1939 and serves as an interstate agreement between New Mexico, Colorado, and Texas to equitably apportion the water of the Rio Grande between the three States and the Republic of Mexico. The Reclamation, USACE, and New Mexico Interstate Stream Commission (NMISC) collectively manage the water facilities in the Upper Rio Grande basin, which comprises the Rio Grande from its headwaters in Colorado through New Mexico to just above Fort Quitman, Texas. Of the 10 total facilities, 5 are located on tributaries: Heron and El Vado Reservoirs operated by Reclamation; Platoro Reservoir operated by a local provider; and Abiquiu and Jemez Canyon Reservoirs operated by the USACE. The remaining five facilities are on the mainstem of the Rio Grande, including the Closed Basin Project operated by Reclamation in Colorado, Cochiti Lake operated by the USACE, and the Low Flow Conveyance Channel (LFCC), Elephant Butte, and Caballo Reservoirs operated by Reclamation. The NMISC is responsible for Rio Grande Compact deliveries to Elephant Butte Reservoir and coordinates with Reclamation and the USACE regarding reservoir operations and accounting of native Rio Grande and San Juan-Chama (SJC) Project contract water. Two major Reclamation projects exist in the Upper Rio Grande basin: the Rio Grande Project and the Middle Rio Grande Project. The Rio Grande Project, which is located in southern New Mexico and Texas, delivers a water supply for about 178,000 acres of land and electric power for communities and industries. About 60% of these lands receiving water are in New Mexico and the remaining 40% are in Texas. Water also is provided for diversion to Mexico by the International Boundary and Water Commission-United States Section to irrigate about 25,000 acres in the Juarez Valley. The principal crops in the Rio Grande Project are cotton, alfalfa, vegetables, pecans, and grain. The Middle Rio Grande Project extends along the Rio Grande Valley in central New Mexico from Cochiti Dam to Elephant Butte Reservoir and irrigates between 53,000 and 73,000 acres. The Middle Rio Grande Project was jointly planned by Reclamation and the USACE to rehabilitate the Middle Rio Grande Conservancy District facilities (including El Vado Dam located on the Rio Chama and three diversion structures: Angostura, Isleta, and San Acacia) and to control sedimentation and flooding. 107

23 The principal crops currently being cultivated in the Middle Rio Grande Project are alfalfa and irrigated pasture. In the mid-l990s, two species in the Rio Grande basin (the Rio Grande silvery minnow and the southwestern willow flycatcher) were designated as endangered under the Federal Endangered Species Act. A delicate balance in water management in the basin is required to meet species and habitat needs, manage flows in the highly variable flow regime of the Rio Grande, and satisfy competing water demands. 6.2 Historical Climate Temperature in the Rio Grande basin varies from year to year as well as with topography. Mean annual temperatures increase as elevation decreases as the river flows south from the mountains through the desert in the southern part of the basin. The basin also experiences natural year-to-year variability. th century, warming has been prevalent over the Over the course of the 20 Rio Grande basin. Above Elephant Butte (figure 38), the basin average temperature has increased by approximately 1 2 F during the course of the 2O century. The warming of the Rio Grande basin has not been steady in time throughout the th century. The basin s average temperature increased steadily from roughly the s to the mid-1940s and then declined slightly until the 1970s before increasing steadily through the end of the century (figure 38, top panel). The warming identified is consistent with other findings within the region. In northern New Mexico, recent annual average temperatures have been more than 2 F above th1 century values (D Antonio 2006; Rangwala and Miller 2010). In mid20 particular, the San Juan Mountains, the headwaters of the Rio Grande, appears to have experienced a 1 C increase from with most of the warming occurring during Precipitation in the Rio Grande basin is highly variable; both throughout time as shown in figure 38 and spatially throughout the basin. Most precipitation falls as snow in the mountains in southern Colorado and northern New Mexico; however, summertime precipitation events in the southern portion of the basin also contribute to the total annual precipitation. A slight increase in basin precipitation is evident over the past century (figure 38); however, any change in precipitation appears to be subtle relative to annual variability. 108

24 Mean Temperature tr Rio Grande Basin (Lper and Middle) 12 hrbderdirçinseptemter ci I. I-. ci a E ENDING YEAR OF PERIOD ci, a) -C C) C Total Precipibon for Ro Grande Basin (Upper and Middle) 12 rronth erbderiing in Septemter reeeh C 0 Ct.4- a C) a) ci FEEEEEEEEE C ENDING YEAR OF PERIOD Figure 38. Observed annual (red) and moving-mean annual (blue) temperature and precipitation, averaged over the Rio Grande basin above Elephant Butte. Source: Western Climate Mapping Initiative (WestMap) available at: Westmap/. Red line indicates annual time series for the given geographic region. Blue line indicates 25-year moving annual mean values, where each value is plotted on the center year of its respective 25-year period. WestMap data are derived from the PRISM climate mapping system (Daly et ai. 2004; Gibson et al. 2002). 109

25 6.3 Historical Hydrology Streamfiow in the Rio Grande basin varies significantly from month to month as well as from year to year. The majority of the annual streamfiow in the Rio Grande basin comes in spring and early summer as a result of snowmelt. Streamfiow is lowest in late summer and fall; however, flows can be temporarily augmented by runoff from localized monsoon precipitation events. Changes in snowpack in the basin have been studied with results that appear to be sensitive to the time-period analyzed. April 1st SWE increased over the latter half of the century ( ) (Regonda 2005; Mote 2006); however, over the relatively shorter period , April 1st SWE appears to have decreased (Enquist et al. 2008). Changes in April 1St SWE are important to understand because they could be indicative of more precipitation falling as rain and less falling as snow or earlier snowmelt. If trends in historical runoff within the basin are to be considered, review of historical data shows that some runoff trends may be apparent depending on location and period of record being assessed. However, evaluation of such trends suggests they are relatively weak. Other studies have found trends that are more significant depending on location, period, and runoff aspect considered. For example, the timing and origin of runoff in the Rio Grande basin appears to have been changing over the past century, trending toward earlier springtime snowmelt (Stewart et al. 2005; Enquist et al. 2008) and increased streamfiow in winter months (Passell et al. 2004). The timing of peak runoff across northern New Mexico over the past half century occurred on average 7 days earlier when compared with the first half of the century (Stewart et al. 2005; Enquist et al. 2008). In addition, streamfiow in the winter months of January, February, and March has increased over the last quarter century relative the century as a whole (Passell et al. 2004). Streamfiow reconstructions based on tree rings have suggested that, in terms of annual streamfiow volume, the second half of the 20 th century was fairly representative of the long-term average hydrology and range of variability, but the period from is wetter than the long-term average (Lewis and Hathaway 2002). 8 8 Trend significance was assessed using statistical testing during the period of applied to historical simulated runoff results under observed historical weather conditions (Reclamation 201 la). Trends were computed and assessed for four Missouri basin locations, focusing on annual and April July runoff. In all cases, computed trends were judged to not be statistically significant with 95% confidence. 110

26 6.4 Future Changes in Climate and Hydrology This section summarizes results from studies focused on future climate and hydrologic conditions within the Rio Grande basin. Emphasis in this discussion is placed on the snowmelt-driven Upper Rio Grande. Discussion first focuses on results from Reclamation (201 la), which were produced within the context of a west-wide hydrologic analysis to identify risks to water supplies in a consistent manner throughout the eight major river basins identified within the SECURE Water Act. These results are discussed separately from those of other studies to set up easier comparison with future climate and hydrology results found in the other basins reported on in this document Projections of Future Climate This section initially summarizes climate projections and climate change assumptions featured within Reclamation (201 la). Climate information is first presented from the perspective of basin average and, secondly, as those climate conditions are distributed throughout the basin. A summary of snow-related effects under future climate conditions as they may be distributed throughout the basin is then presented; and, finally, climate and snowpack changes translated into effects on annual and seasonal runoff as well as acute runoff events relevant to flood control and ecosystems management are discussed. Before summarizing climate projection and climate change information, it is noted that the projected changes have geographic variation, they vary through time, and the progression of change through time varies among climate projection ensemble members. Starting with a regional view of the time series climate projections and drawing attention to the projections median condition through time, results suggest that temperatures throughout the Rio Grande basin may increase steadily during the 21 century. The basin-average mean-annual temperature is projected to increase by roughly 5 6 F during the 21 century in the Upper Rio Grande basin. The range of annual possibility widens through time. St The ensemble mean of projections indicates that mean-annual precipitation, averaged over either subbasin presented for the Upper Rio Grande basin (figure 39), may gradually decrease during the 21st century. This is evident by following the ensemble median of the annual precipitation through time for both basins. The projections also suggest that annual precipitation in the Rio Grande basin will remain quite variable over the next century. Despite the previous statement about the ensemble mean, there is significant disagreement among the climate projections regarding change in annual precipitation over the region. St 111

27 Rio Chama near Abiquiu Water Year Rio Chama near Abiquiu 20 E1EI11 Rio Grande near Otowi Water Year Rio Grande near Otowi 20 : Water Year 20 - :::::z:il:ii..j Water Year Figure 39. Simulated annual climate averaged over Rio Grande subbasins. Figure 39 displays the ensemble of temperature and precipitation projections from Bias Corrected and Spatially Downscaled WCRP CMIP3 Climate Projections (section 1.5.1). Annual conditions represent spatially averaged results over the basin. Darker colored lines indicate the median-annual condition through time, sampled from the ensemble of 112 climate simulations (section 1.5.1), and then smoothed using a 5-year running average. Lighter-colored areas represent the time-series range of lothto 90 th percentile annual values within the ensemble from simulated 1950 through simulated Projection of climate change is geographically complex over the upper Rio Grande basin, particularly for precipitation. For example, consider the four decades highlighted on figure 39 (vertical gray bars): the 1990s, 2020s, 2050s, and 2070s. The 1990s are considered to be the baseline climate from which climate changes will be assessed for the three future decades (2020s, 2050s, and 2070s). The baseline climate indicates that local climate varies considerably within the basin. For example, annual average temperatures are generally cooler in the high-elevation upper reaches in the north and along the mountainous rim (figure 40, top left panel). Warmer temperatures occur to the south and in lower lying areas. Likewise, precipitation is generally greater in the upper reaches along the mountainous rim, and lesser in the lower lying areas and to the south (figure 41, top left panel). Projected temperature changes under projected climate-change scenarios are generally uniform over the basin and steadily increase through time (figure 40). For precipitation, similar geographic 112

28 Rio Grerie at Elepht &*te Oem Mean Arwwial Temperatxe (F) I 990s, EnsembleMedian change i Mean Annual Temperat,e (F) 2020s-1 990s, EnsembleMedian 6 I Change w Mean Annual Temperah.re (F) 2050s-I 990s, Ensemble-Median Change n Mean Annual Temperature (F) 2070s-1 990s, Ensemble-Median 6 I Figure 40. Simulated decade-mean temperature over the Rio Grande basin above Elephant Butte. Figure 40 presents basin-distributed views of change over the given basin and variable. Figure data are simulated conditions as described in Reclamation 201 Ia. Upper left panel shows the baseline mean-annual condition (1990s), and next three panels show changes from baseline conditions for three future decades (2020s, 2050s, and 2070s). Both historical and future conditions are from climate simulations (section 1.5.1). Mapped values for baseline conditions (1990s) are median-values from the collection of climate simulations. Mapped changes (next three panels) are median changes from the collection of climate simulations. Temperature units F for baseline and change. Precipitation and SWE units are inches for baseline and percentage for change. For SWE, areas that are white on the plots have less 1990s decade-mean conditions of less than inch and are not considered in the change assessment. 113

29 Rio Grande at EleØw &4te Dn Mean Annual Prec ion (iches) 1 990s, Ensen*ean change ii Mean Anal Precitation (%) 2020s-1 990s, Enseuan Change in Mean Annual Precipitation (%) 2050s-1 990s, Ensemble-Median i20 10 Change n Mean Annual Precdation (%) 2070s-1 990s, Ensentle-Meckan 20 II Figure 41. Simulated decade-mean precipitation over the Rio Grande basin above Elephant Butte. Figure 41 presents basin-distributed views of change over the given basin and variable. Figure data are simulated conditions as described in Reclamation a. Upper left panel shows the baseline mean-annual condition (1990s), and next three panels show changes from baseline conditions for three future decades (2020s, 2050s, and 2070s). Both historical and future conditions are from climate simulations (section 1.5.1). Mapped values for baseline conditions (1990s) are median-values from the collection of climate simulations. Mapped changes (next three panels) are median changes from the collection of climate simulations. Temperature units F for baseline and change. Precipitation and SWE units are inches for baseline and percentage for change. For SWE, areas that are white on the plots have less 1990s decade-mean conditions of less than inch and are not considered in the change assessment. 114

30 consistency is found, although there is less uniformity during the earlier part of the 2l century decades. Overall, precipitation is projected to gradually decline over much of the basin during the course of the 2l century. Despite the overall magnitude of precipitation under increasing temperature projections, the character of precipitation within the Upper Rio Grande basin is expected to change under warming conditions, resulting in more frequent rainfall events and less frequent snowfall events. Temperature and precipitation changes are expected to affect hydrology in various ways including snowpack development. As noted previously, warming is expected to diminish the accumulation of snow during the cool season (i.e., late autumn through early spring) and the availability of snowmelt to sustain runoff to the Upper Rio Grande during the warm season (i.e., late spring through early autumn). Although increases or decreases in cool season precipitation could somewhat offset or amplify changes in snowpack, it is apparent that the projected warming in the Upper Rio Grande basin tends to dominate projected effects (e.g., changes in April 1st snowpack distributed over the basin, shown on figure 42). Snowpack decreases are expected to be more substantial over the portions of the basin where baseline cool season temperatures are generally closer to freezing thresholds and more sensitive to projected warming. This is particularly the case for the lower lying areas of the basin. Changes in climate and snowpack within the Upper Rio Grande basin will change the availability of natural water supplies. These changes may be due to annual runoff, and also changes in runoff seasonality. For example, warming without precipitation change would lead to increased evapotranspiration from the watershed and decreased annual runoff. Precipitation increases or decreases (either as rainfall or snowfall) would offset or amplify the effect. Results from Reclamation ( a) suggest that annual runoff changes are generally consistent but do vary slightly by location in the Upper Rio Grande basin (figure 42), depending on baseline climate and the projected temperature and precipitation changes. For example, annual runoff reductions in the Rio Chama at Abiqiu, draining the northwestern reaches of the basin, are projected to be somewhat less than reductions found at river locations draining the northern and eastern portions of the basin. However, at all locations, decade-mean annual runoff is projected to steadily decline through the 21 St century, responding to both slight decreases in precipitation and warming over the region. The seasonality of runoff is also projected to change in the Upper Rio Grande. Warming would be expected to lead to more rainfall and runoff, rather than snowpack accumulation, during the winter. Conceptually, this change would lead to increases in the December March runoff and decreases in the April July 115

31 Ro Grande Elephaii te Dan Mean Api 1st W (nches) 1 990s, senemean change ri Mean AprI 1st S* (%) 2020s-1 990s, eman I Change r Mean April 1st Sf (%) 2050s-1 9s, Ensemble-Median 100 Change in Mean Api 1st SE (%) 2070s-1 990s, Ensemble-Median o Figure 42. Simulated decade-mean April Elephant Butte st snowpack over the Rio Grande basin above Figure 42 presents basin-distributed views of change over the given basin and variable. Figure data are simulated conditions as described in Reclamation a. Upper left panel shows the baseline mean-annual condition (1990s), and next three panels show changes from baseline conditions for three future decades (2020s, 2050s, and 2070s). Both historical and future conditions are from climate simulations (section 1.5.1). Mapped values for baseline conditions (1990s) are median-values from the collection of climate simulations. Mapped changes (next three panels) are median changes from the collection of climate simulations. Temperature units F for baseline and change. Precipitation and SWE units are inches for baseline and percentage for change. For SWE, areas that are white on the plots have less 1990s decade-mean conditions of less than inch and are not considered in the change assessment. 116

32 runoff. However, results from across the upper Rio Grande basin suggest that the degree to which this concept is consistent with projections depends on the location of interest (figure 43). The concept is supported by results for the December March seasonal runoff in the Rio Chama at Abiquiu, as mean seasonal runoff increases for each of the three future decades. However, for the three locations shown on the Rio Grande (Rio Grande at Lobatos, Rio Grande at Lobatos, and Rio Grande at Elephant Butte), mean seasonal runoff changes during December March generally follow mean annual runoff changes, without this shift from April July to December March runoff. However, at all four of the locations shown on figure 43, mean April July runoff is expected to decline, and these declines are expected to become greater in magnitude over the course of the 2 century. It may be noticed that percentage reductions in April July runoff may appear to be small compared to some percentage reductions in lower elevation April 1st snowpack from the preceding discussion. The fact that percentage April July runoff reductions are smaller speaks to how higher elevation snowpack contributes proportionally more to April July runoff than lower elevation snowpack, and how percentage snow losses at higher elevations are relatively smaller than those at lower elevation. Changes in the magnitude of flood peaks also are expected in the Upper Rio Grande, although there is less certainty in the analysis of these types of acute events than there is for changes in annual or seasonal runoff. Annual maximumand minimum-week runoff, as metrics of acute runoff events (figure 44), indicate st century. that annual maximum-week runoff may gradually decline during the 21 Results are generally consistent across the subbasins shown. These results suggest that future flood events in the Rio Grande may be smaller in magnitude than those experienced in the 1 990s, although the streamfiow variability is expected to continue to be large. These changes have implications for flood control and ecosystem management. However, it is important to note that there is a high degree of variability among model simulations suggesting there is a high degree of uncertainty in this flood metric. For annual minimum-week runoff, similar consistency is found across the st century. These results subbasins, also showing projected declines during the 21 suggest that future low flow periods in the Rio Grande may be drier still looking into the future. Decreasing annual minimum runoff may reduce available diversions for agricultural, municipal, and industrial uses. Decreasing minimum runoff also adversely affects aquatic habitats through reduced wetted stream perimeters and availability of aquatic habitat and through increased water temperatures detrimental to temperature-sensitive aquatic organisms. However, there is a high degree of variability among model simulations suggesting there is a 117

33 Secure Water Act Section 9503(c) high degree of uncertainty in this low flow metric. Nevertheless, nearly all ensemble members project an overall decrease in low flow values, and the uncertainty lies in the magnitude of this trend. A summary of climate and hydrologic changes is provided in table 5 for three subbasins of the Upper Rio Grande basin: Rio Chama at Abiquiu, Rio Grande near Otowi, and Rio Grande at Elephant Butte Dam. The tabulated changes reflect a subbasin-average view and are measured relative to l990s baseline conditions, as shown on the preceding figures. Rio Grande near Lobatos Rio Chama near Abiquiu C Li 0) Dl C-) 0) 0 Dl -10.J..L L fl -20 I Annual Dec-Mar Apr-Jul -20 I 2LO - Annual Dec-Mar Apr-Jul 10 Rio Grande near Otowi 10 Rio Grande at Elephant Eutte Dam C a3 0 C-) l) 1.) -20 I Annual Dec-Mar Apr-Jul C -E C) L Li Annual Dec-Mar Apr-Jul Figure 43. Simulated changes in decade-mean runoff for several subbasins in the Rio Grande basin. Figure 43 presents annual, December March, and April July runoff impacts for subbasins shown. Each panel shows percentage changes in mean runoff (annual or either season) for three future decades (2020s, 2050s, and 2070s) relative to baseline conditions (1990s). Development of runoff information is described in Reclamation (201 la) based on climate simulations previously discussed (section 1.5.1). 118

34 I: Rio Grande near Lobatos C) 0 C Rio Grande near Lobatos x C) SI Water Year Rio Grande near Otowi Water Year 0 C I Water Year Rio Grande near Otowi Water Year C) Rio Grande at Elephant Butte Dam Water Year Water Year Figure 44. Simulated annual maximum and minimum week runoff for several subbasins in the Rio Grande River basin. Figure 44 displays the ensemble of annual maximum 7-day and minimum 7-day runoff projections for the subbasins shown development of runoff information is described in Reclamation ( a) based on climate simulations previously discussed (section 1.5.1). It should be noted that these results are derived from simulations that have been computed at a daily time step but have been calibrated to monthly natural flows. As such, there is considerable uncertainty that is reflected in the lightly shaded regions around the heavier dark line. These values are presented for qualitative, rather than quantitative analysis. 0 C :3 Ix I